The invention generally relates to vacuum processing systems and methods and, in particular, to mechanisms and methods for improving material uniformity in the chemical vapor and physical vapor deposition systems.
Due to the current growth in the LED and OLED markets, there is an ever increasing demand for efficient and high throughput manufacturing methods and systems. Current high throughput manufacturing systems use chemical vapor deposition (CVD) to deposit material on several substrate wafers simultaneously and thus to maximize their throughput. Yield per wafer is typically related to the uniformity of the deposition on it, with a more uniform deposition resulting in a higher yield.
In the past and current CVD systems, the means for achieving improved uniformity included heating of a wafer carrier, varying shape of a reaction chamber, modifying shower head characteristic as well as rotating the wafer carrier. All of these methods were used with varying degree of success with much improvement still needed. In particular, when rotating a wafer carrier containing multiple substrate wafers it is desirable to rotate it at a rate different from that of the wafers, thereby creating planetary motion. This allows a greater control over a deposition profile as well real time correction of various defects in the deposition's uniformity.
Currently available methods for creating planetary motion of the wafers on a wafer carrier include continuously driven planetary gearing system, application of circulating gasses under the substrate and vibration of the wafer carrier to induce rotation of the wafers. Each of these systems has its own drawbacks. A typical continuously driven planetary gearing system consists of a set of gears which continuously drive both a plurality of wafer platforms and the wafer carrier. The gears of the mechanism are continuously loaded by both the mass of the wafer carrier and the mass of plurality of wafer platforms. Addition of the thermal stress due to high operational temperatures adds to the mechanical stress in the mechanism and results in lower reliability and higher particle generation. Planetary motion through application of circulating gases limits operation of the wafers carrier to the low rpm range in order to maintain planetary motion as well as degrades CVD process performance by interfering with the reaction gases and increasing the total gas load on the system's pump. The use of vibration to create planetary motion does not guarantee equal magnitude of rotation for all of the wafers on the wafer carrier as well as limits possible wafer carrier rotation rates.
Thus, there is a need for a mechanism which improves deposition uniformity without negative impacts on maintenance and operational rpm of the wafer carrier. The mechanism must also ensure equal magnitude of rotation among all of the wafers on the wafer carrier.